Dual voltage battery system for a vehicle

ABSTRACT

A power management system for a vehicle includes a first battery monitoring module configured to monitor a first state of charge (SOC) of a first battery of the vehicle. The first battery has a first nominal voltage. A second battery monitoring module is configured to monitor a second SOC of a second battery of the vehicle. The second battery has a second nominal voltage that is greater than the first nominal voltage. A control module is configured to selectively apply power to a heater of the second battery based on an estimated value of the second SOC of the second battery at a next startup of an engine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/910,663, filed on Mar. 2, 2018, which claims the benefit of U.S.Provisional Application No. 62/466,954, filed on Mar. 3, 2017. Theentire disclosures of the applications referenced above are incorporatedherein by reference.

FIELD

The present disclosure relates to battery systems for vehicles and moreparticularly dual voltage battery systems for vehicles.

BACKGROUND

The background description provided here is for the purpose of generallypresenting the context of the disclosure. Work of the presently namedinventors, to the extent it is described in this background section, aswell as aspects of the description that may not otherwise qualify asprior art at the time of filing, are neither expressly nor impliedlyadmitted as prior art against the present disclosure.

Vehicle battery systems are an important component of a vehicle. If thecapacity of the battery is too small, the vehicle may be unable to startan engine in cold weather. If the capacity of the battery is increased,a footprint of the battery and/or the cost of the battery also typicallyincrease. Current battery systems typically operate at 12V (Volt). Forvehicles such as hybrid vehicles, there are advantages associated withmoving to higher voltage battery systems such as battery systemsoperating at 48V. However, many of the vehicle components were designedto operate at 12V so it is difficult to switch production to the highervoltage battery system all at once. Some vehicles have a dual voltagebattery system including a first battery operating at a first voltagelevel such as 12V and a second battery operating at a higher voltagelevel such as 48V.

SUMMARY

In a feature, a power management system for a vehicle is described. Afirst battery monitoring module is configured to monitor a first stateof charge (SOC) of a first battery of the vehicle. The first battery hasa first nominal voltage. A second battery monitoring module isconfigured to monitor a second SOC of a second battery of the vehicle.The second battery has a second nominal voltage that is greater than thefirst nominal voltage. A control module is configured to, using a directcurrent (DC) to DC converter, selectively charge the second battery withpower from the first battery until the second SOC of the second batteryis greater than or equal to a predetermined SOC.

In further features, a starter control module is configured toselectively apply power to a starter of an engine from the secondbattery.

In further features, the control module is configured to selectivelycharge the second battery with power from the first battery when thesecond SOC of the second battery at shutdown of an engine of the vehicleis less than the predetermined SOC.

In further features, the control module is configured to: determinewhether to charge the second battery with power from the first batterybased on an ambient temperature at shutdown of an engine; andselectively charge the second battery with power from the first batterybased on the determination.

In further features, the control module is further configured to, priorto a startup of an engine of the vehicle, selectively apply power to aheater of the second battery based on a temperature of the secondbattery and the SOC of the second battery.

In further features, the control module is configured to, prior to thestartup of the engine of the vehicle, apply power to the heater of thesecond battery when the temperature of the second battery is less than apredetermined temperature.

In further features, the control module is configured to, prior to thestartup of the engine of the vehicle, apply power to the heater of thesecond battery from the first battery when: the temperature of thesecond battery is less than a predetermined temperature; and the secondSOC of the second battery is less than the predetermined SOC.

In further features, the control module is further configured to, priorto a startup of an engine of the vehicle, using the DC to DC converter,charge the first battery with power from the second battery when thesecond SOC of the second battery is greater than a second predeterminedSOC.

In further features, the second predetermined SOC is greater than thepredetermined SOC.

In further features, the control module is configured to: in response toa shutdown of an engine of the vehicle, determine an estimatedtemperature at a next startup of the engine; determine whether to chargethe second battery with power from the first battery based on theestimated temperature; and selectively charge the second battery withpower from the first battery based on the determination.

In further features, the control module is configured to set theestimated temperature at the next startup of the engine based on anambient temperature at the shutdown of the engine.

In further features, the control module is configured to set theestimated temperature at the next startup of the engine based on anambient temperature obtained in response to the shutdown of the engineminus a predetermined temperature.

In further features, the control module is configured to determine theestimated temperature at the next startup of the engine based on anaverage temperature at a location of the vehicle at the next startup ofthe engine.

In further features, the control module is configured to determine theestimated temperature at the next startup of the engine based on aforecast temperature at a location of the vehicle at the next startup ofthe engine.

In further features, the control module is configured to determine theestimated temperature at the next startup of the engine based on aplurality of previous temperatures at previous startups of the engineperformed near a location of the vehicle, respectively.

In further features, the control module is configured to determine tocharge the second battery with power from the first battery when, basedon the estimated temperature at the next startup of the engine, anestimated value of the second SOC of the second battery at the nextstartup of the engine is less than the predetermined SOC.

In further features, the control module is configured to: in response toa shutdown of an engine of the vehicle, determine an estimatedtemperature at a next startup of the engine; determine an ambienttemperature at the next startup of the engine; and selectively applypower to a heater of the second battery based on a comparison of theestimated temperature at the next startup of the engine and the ambienttemperature at the next startup of the engine.

In further features, the control module is configured to selectivelyapply power from only the second battery to the heater when theestimated temperature at the next startup of the engine is greater thanthe ambient temperature at the next startup of the engine.

In further features, the control module is configured to selectivelyapply power from both the first battery and the second battery to theheater when the estimated temperature at the next startup of the engineis less than the ambient temperature at the next startup of the engine.

In a feature, a power management method for a vehicle includes:monitoring a first state of charge (SOC) of a first battery of thevehicle, where the first battery has a first nominal voltage; monitoringa second SOC of a second battery of the vehicle, where the secondbattery has a second nominal voltage that is greater than the firstnominal voltage; and, using a direct current (DC) to DC converter,selectively charging the second battery with power from the firstbattery until the second SOC of the second battery is greater than orequal to a predetermined SOC.

In further features, the power management method further includesselectively applying power to a starter of an engine from the secondbattery.

In further features, the selectively charging the second batteryincludes selectively charging the second battery with power from thefirst battery when the second SOC of the second battery at shutdown ofan engine of the vehicle is less than the predetermined SOC.

In further features, the power management method further includes:determining whether to charge the second battery with power from thefirst battery based on an ambient temperature at shutdown of an engine,where the selectively charging the second battery includes selectivelycharging the second battery with power from the first battery based onthe determination.

In further features, the power management method further includes, priorto a startup of an engine of the vehicle, selectively applying power toa heater of the second battery based on a temperature of the secondbattery and the SOC of the second battery.

In further features, the selectively applying power to the heaterincludes, prior to the startup of the engine of the vehicle, applyingpower to the heater of the second battery when the temperature of thesecond battery is less than a predetermined temperature.

In further features, the selectively applying power to the heaterincludes, prior to the startup of the engine of the vehicle, applyingpower to the heater of the second battery from the first battery when:the temperature of the second battery is less than a predeterminedtemperature; and the second SOC of the second battery is less than thepredetermined SOC.

In further features, the power management method further includes, priorto a startup of an engine of the vehicle, using the DC to DC converter,charging the first battery with power from the second battery when thesecond SOC of the second battery is greater than a second predeterminedSOC.

In further features, the second predetermined SOC is greater than thepredetermined SOC.

In further features, the power management method further includes: inresponse to a shutdown of an engine of the vehicle, determining anestimated temperature at a next startup of the engine; and determiningwhether to charge the second battery with power from the first batterybased on the estimated temperature, where the selectively charging thesecond battery includes selectively charging the second battery withpower from the first battery based on the determination.

In further features, the determining the estimated temperature includessetting the estimated temperature at the next startup of the enginebased on an ambient temperature at the shutdown of the engine.

In further features, the determining the estimated temperature includessetting the estimated temperature at the next startup of the enginebased on an ambient temperature obtained in response to the shutdown ofthe engine minus a predetermined temperature.

In further features, the determining the estimated temperature includesdetermining the estimated temperature at the next startup of the enginebased on an average temperature at a location of the vehicle at the nextstartup of the engine.

In further features, the determining the estimated temperature includesdetermining the estimated temperature at the next startup of the enginebased on a forecast temperature at a location of the vehicle at the nextstartup of the engine.

In further features, the determining the estimated temperature includesdetermining the estimated temperature at the next startup of the enginebased on a plurality of previous temperatures at previous startups ofthe engine performed near a location of the vehicle, respectively.

In further features, the determining whether to charge the secondbattery includes determining to charge the second battery with powerfrom the first battery when, based on the estimated temperature at thenext startup of the engine, an estimated value of the second SOC of thesecond battery at the next startup of the engine is less than thepredetermined SOC.

In further features, the power management method further includes: inresponse to a shutdown of an engine of the vehicle, determining anestimated temperature at a next startup of the engine; determining anambient temperature at the next startup of the engine; and selectivelyapplying power to a heater of the second battery based on a comparisonof the estimated temperature at the next startup of the engine and theambient temperature at the next startup of the engine.

In further features, the selectively applying power to the heaterincludes selectively applying power from only the second battery to theheater when the estimated temperature at the next startup of the engineis greater than the ambient temperature at the next startup of theengine.

In further features, the selectively applying power to the heaterincludes selectively applying power from both the first battery and thesecond battery to the heater when the estimated temperature at the nextstartup of the engine is less than the ambient temperature at the nextstartup of the engine.

In a feature, a power management system for a vehicle includes a firstbattery monitoring module configured to monitor a first state of charge(SOC) of a first battery of the vehicle. The first battery has a firstnominal voltage. A second battery monitoring module is configured tomonitor a second SOC of a second battery of the vehicle. The secondbattery has a second nominal voltage that is greater than the firstnominal voltage. A control module is configured to selectively applypower to a heater of the second battery based on an estimated value ofthe second SOC of the second battery at a next startup of an engine.

In further features, a starter control module is configured toselectively apply power to a starter of the engine from the secondbattery at the next startup of the engine.

In further features, the control module is configured to apply power tothe heater of the second battery when the estimated value of the secondSOC of the second battery at the startup of the engine is less than apredetermined SOC.

In further features, the control module is configured to: in response toa shutdown of an engine of the vehicle, determine an estimatedtemperature at the next startup of the engine; and determine theestimated value of the second SOC of the second battery based on theestimated temperature at the next startup of the engine.

In further features, the control module is configured to set theestimated temperature at the next startup of the engine based on anambient temperature at the shutdown of the engine.

In further features, the control module is configured to set theestimated temperature at the next startup of the engine based on anambient temperature obtained in response to the shutdown of the engineminus a predetermined temperature.

In further features, the control module is configured to determine theestimated temperature at the next startup of the engine based on anaverage temperature at a location of the vehicle at the next startup ofthe engine.

In further features, the control module is configured to determine theestimated temperature at the next startup of the engine based on aforecast temperature at a location of the vehicle at the next startup ofthe engine.

In further features, the control module is configured to determine theestimated temperature at the next startup of the engine based on aplurality of previous temperatures at previous startups of the engineperformed near a location of the vehicle, respectively.

In further features, the control module is configured to: in response toa shutdown of an engine of the vehicle, determine an estimatedtemperature at the next startup of the engine; determine an ambienttemperature at the next startup of the engine; and selectively applypower to the heater of the second battery based on a comparison of theestimated temperature at the next startup of the engine and the ambienttemperature at the next startup of the engine.

In further features, the control module is configured to selectivelyapply power from only the second battery to the heater when theestimated temperature at the next startup of the engine is greater thanthe ambient temperature at the next startup of the engine.

In further features, the control module is configured to selectivelyapply power from both the first battery and the second battery to theheater when the estimated temperature at the next startup of the engineis less than the ambient temperature at the next startup of the engine.

In a feature, a power management method for a vehicle includes:monitoring a first state of charge (SOC) of a first battery of thevehicle, where the first battery has a first nominal voltage; monitoringa second SOC of a second battery of the vehicle, where the secondbattery has a second nominal voltage that is greater than the firstnominal voltage; and selectively applying power to a heater of thesecond battery based on an estimated value of the second SOC of thesecond battery at a next startup of an engine.

In further features, the power management method further includesselectively applying power to a starter of the engine from the secondbattery at the next startup of the engine.

In further features, the selectively applying power to the heaterincludes applying power to the heater of the second battery when theestimated value of the second SOC of the second battery at the startupof the engine is less than a predetermined SOC.

In further features, the power management method further includes: inresponse to a shutdown of an engine of the vehicle, determining anestimated temperature at the next startup of the engine; and determiningthe estimated value of the second SOC of the second battery based on theestimated temperature at the next startup of the engine.

In further features, the determining the estimated temperature includessetting the estimated temperature at the next startup of the enginebased on an ambient temperature at the shutdown of the engine.

In further features, the determining the estimated temperature includessetting the estimated temperature at the next startup of the enginebased on an ambient temperature obtained in response to the shutdown ofthe engine minus a predetermined temperature.

In further features, the determining the estimated temperature includesdetermining the estimated temperature at the next startup of the enginebased on an average temperature at a location of the vehicle at the nextstartup of the engine.

In further features, the determining the estimated temperature includesdetermining the estimated temperature at the next startup of the enginebased on a forecast temperature at a location of the vehicle at the nextstartup of the engine.

In further features, the determining the estimated temperature includesdetermining the estimated temperature at the next startup of the enginebased on a plurality of previous temperatures at previous startups ofthe engine performed near a location of the vehicle, respectively.

In further features, the power management method further includes: inresponse to a shutdown of an engine of the vehicle, determining anestimated temperature at the next startup of the engine; and determiningan ambient temperature at the next startup of the engine, where theselectively applying power to the heater includes selectively applyingpower to the heater of the second battery based on a comparison of theestimated temperature at the next startup of the engine and the ambienttemperature at the next startup of the engine.

In further features, the selectively applying power to the heaterincludes selectively applying power from only the second battery to theheater when the estimated temperature at the next startup of the engineis greater than the ambient temperature at the next startup of theengine.

In further features, the selectively applying power to the heaterincludes selectively applying power from both the first battery and thesecond battery to the heater when the estimated temperature at the nextstartup of the engine is less than the ambient temperature at the nextstartup of the engine.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1A is a functional block diagram of an example of a powermanagement system for supplying power from a first battery and a secondbattery operating at different voltages according to the presentdisclosure;

FIG. 1B is a more detailed functional block diagram of an example of apower management module in FIG. 1A according to the present disclosure;

FIGS. 2 and 3 are graphs showing power as a function of state of charge(SOC) at first and second temperatures (25° C. and 0° C., respectively)according to the present disclosure;

FIG. 4 is a flowchart illustrating an example of a method for movingenergy from the first battery to the second battery in response to a keyoff event based upon ambient temperature according to the presentdisclosure;

FIG. 5 is a flowchart illustrating an example of a method forcontrolling energy in the first battery and the second battery after akey on event according to the present disclosure;

FIG. 6 is a flowchart illustrating an example of a method for movingenergy from the first battery to the second battery based upon ambienttemperature minus a predetermined temperature drop according to thepresent disclosure;

FIG. 7 is a flowchart illustrating an example of a method for movingenergy from the first battery to the second battery based upon ambienttemperature at the next key on (estimated based on prior usage)according to the present disclosure;

FIG. 8 is a flowchart illustrating an example of a method for creating ausage pattern or model for the vehicle based on information stored aftera plurality of key on events according to the present disclosure;

FIG. 9 is a flowchart illustrating an example of a method for estimatingambient temperature during a next key on event based upon the usagepattern or model according to the present disclosure;

FIGS. 10 and 11 are flowchart illustrating examples of methods formoving energy based on the SOC of the second battery according to thepresent disclosure; and

FIG. 12 is a flowchart illustrating a method for moving energy betweenthe first battery and the second battery based on a comparison of theactual ambient temperature during the key on event and the estimatedambient temperature according to the present disclosure.

In the drawings, reference numbers may be reused to identify similarand/or identical elements.

DETAILED DESCRIPTION

Systems and methods according to the present disclosure relate to a dualvoltage battery system including a first battery and a second batteryoperating at different voltage levels. For example, the first batterymay operate at 12V and the second battery may operate at 48V, althoughother voltage levels may be used. In some examples, energy from thefirst battery is selectively moved to the second battery in response toa key off event to allow the second battery to perform heating prior toa key on event and start the engine while maintaining sufficient energyor state of charge (SOC) in the second battery.

In some examples, the first battery supports a first boardnet supplyingpower to vehicle loads operating at the first voltage level. The secondbattery supports a second boardnet supplying power to vehicle loadsoperating at the second voltage level and sufficient energy to start thevehicle in response to key-on and re-start events. Since the onlypurpose of the first battery in this example is to support the firstboardnet (and not start the vehicle), it is not critical to have thefirst battery operating at 100% state of charge (SOC) during the key-onevent since the alternator can be used to charge the first battery afterstarting.

In other examples, the systems and methods described herein can also beapplied to dual voltage battery systems where the first battery is usedto support the first boardnet and to start the vehicle during a key-onevent. In this case, the systems and methods described herein ensurethat the first battery always has sufficient energy or SOC to heat thefirst battery and to start the vehicle in response to the key-on event.In other words, energy is shuttled from the second battery to the firstbattery as needed.

In some examples, energy is moved from the first battery to the secondbattery (or vice versa) as needed to ensure a sufficient amount ofenergy for heating the second battery (or the first battery) to apredetermined temperature at the next key on.

In some examples, the amount of energy is determined based oninformation including at least one of battery state of charge (SOC),ambient temperature, global positioning system (GPS) information, timeof year (e.g., calendar date), average or current local temperature,and/or time of day. In some examples, the information is used toestimate the amount of energy required to heat the second battery (orthe first battery) to a predetermined temperature such as 25° C., startthe engine, and remain within an optimal SOC range.

Referring now to FIG. 1A, a power management system 100 for controllingthe supply of power from a first battery 108 and a second battery 110 isshown. While a specific example of the power management system 100 isshown, other architectures can be used. In some examples, the firstbattery 108 includes a 12V (nominal) battery with multiple battery cellsconnected in series and/or parallel to positive and negative batteryterminals, although other voltage levels can be used. In some examples,the second battery 110 includes a 48V battery with multiple batterycells connected in series and/or parallel to positive and negativebattery terminals, although other voltage levels can be used. In someexamples, the second battery 110 operates at a higher (nominal) voltagethan the first battery 108. In some examples, the second battery 110operates at 24V, 36V, or 48V nominal (0-54 V), although other voltagelevels can be used.

A power management module 112 controls the supply of power from thefirst battery 108 and the second battery 110. The power managementmodule 112 may communicate over a vehicle data bus 114 with othervehicle controllers and/or with components of the power managementsystem 100. The power management module 112 may transmit data such asstate of charge (SOC) and state of health (SOH) for the first battery108 and the second battery 110 to other vehicle controllers. In someexamples, the vehicle data bus 114 includes a CAN bus, although otherdata bus types can be used. In some examples, the power managementmodule 112 receives information such as key-on events, vehicle speed,drive mode events, engine oil temperature, or other control informationfrom other vehicle controllers. The power management module 112 mayadjust operation of the power management system 100 based on thesesignals.

In some operating modes, the power management module also controls thesupply of current to a vehicle power bus 102 and vehicle loads 104 suchas boardnet loads. The power management module 112 receives batteryoperating parameters from one or more sensors 128 such as temperaturesensors 130 and/or voltage sensors 132. In some examples, thetemperature sensors 130 and the voltage sensors 132 monitor temperaturesand voltages at the battery cell level. The power management module 112also receives operating parameters from sensors 134 such as temperaturesensors 136 and/or voltage sensors 138 associated with the secondbattery 110. In some examples, the temperature sensors 136 and thevoltage sensors 138 monitor temperatures and voltages at the batterycell level.

Temperature control of the second battery 110 may be provided by one ormore heaters, such as heater 142. The heater(s) may be resistiveheaters, thermoelectric devices (TEDs), or another type of heater. Aheater driver circuit 146 controls power supplied to the heater(s). Thepower management module 112 selectively actuates the heater drivercircuit 146 as needed to control the temperature of the first battery108 and/or the second battery 110. In some examples, the heater 142includes one or more zones that allow individual and independenttemperature control of one or more battery cells. The heaters may belocated between individual cells of the second battery 110 or may not belocated between cells of the second battery 110 but arranged to provideheat to one or more of the cells of the second battery 110.

A current detector circuit 150 detects current supplied by the batteryor supplied to the battery during recharging. The current detectorcircuit 150 may be arranged between a negative terminal of the firstbattery 108 and chassis ground 152. A current detector circuit 156detects current supplied by the second battery 110 or supplied to thesecond battery 110 during recharging. The current detector circuit 156may be arranged between a negative terminal of the second battery 110and the chassis ground 152. The current detector circuits 150 and 156provide sensed battery current and current values, respectively, to thepower management module 112.

An overvoltage protection circuit 160 may be arranged between a positiveterminal of the first battery 108 and loads such as the vehicle powerbus 102. The overvoltage protection circuit 160 monitors a voltageoutput of the battery and provides a voltage value to the powermanagement module 112. The overvoltage protection circuit 160 protectsthe battery from overcharging when one or more cells are at or above avoltage limit of the battery cell. Another function of the overvoltageprotection circuit 160 is to protect the battery from excessive current.If an over voltage condition is detected, the first battery 108 may bedisconnected or other actions may be taken.

In some examples, the power management module 112 performs batterymanagement including cell voltage measurement, cell balancing,temperature measurement, current limits calculations, state of charge(SOC) estimation and/or state of health (SOH) estimation based on themeasured battery parameters.

A DC/DC converter 161 may be provided to control flow of the currentbetween the first battery 108, the second battery 110 and/or astarter/generator 174. In some examples, the DC/DC converter 161includes a DC/DC boost converter 162 and a DC/DC buck converter 164 thatare connected between the first battery 108, the second battery 110 andthe starter/generator 174. In some examples, the DC/DC boost converter162 has an input range of 8V to 16V and a current input range of 0-100Amps. In some examples, the DC/DC boost converter 162 has an outputrange of 24V to 54V and a current output range of 0-67 Amps.

In some examples, the DC/DC buck converter 164 has an input range of 24Vto 54V and a current input range of 0-53 Amps. In some examples, theDC/DC buck converter 164 has an output range of 8V to 16V and a currentoutput range of 0-80 Amps. As can be appreciated, the ratings of theDC/DC boost converter 162 and the DC/DC buck converter 164 will vary fordifferent applications.

A starter/generator controller (a starter control module) 170 isconnected to the DC/DC boost converter 162, the DC/DC buck converter164, and the second battery 110. The starter/generator controller 170 isalso connected to a DC/AC converter 172, which is connected to thestarter/generator 174. The starter/generator 174 is connected to anengine (not shown). In some examples, one or more electric motors 175for driving the wheels may be provided.

The vehicle power bus 102 may also be connected to an electric turbo 184and/or an active suspension system 186, which operate at the voltage ofthe first battery 108. Alternately, an electric turbo 180 and/or anactive suspension system 182 may be connected to the starter/generatorcontroller 170 or the AC/DC converter if they operate at higher voltagessuch as 24V, 36V, 48V, etc.

In some examples, a key-on starter 176 may be connected to thestarter/generator controller 170 and may be provided for starting largerdisplacement engines requiring higher starting current. The key-onstarter 176 may be supplied by current from the second battery 110 andassisted in a limited and controlled manner by current supplied by thefirst battery 108 as described above.

In some examples, a global positioning system (GPS) 187 may be used todetermine the location of the vehicle. A network connector 189 providesa wireless connection to a network such as the Internet. In someexamples, the network connector 189 includes a cellular transceiver, asatellite transceiver or other transceiver.

Referring now to FIG. 1B, an example of the power management module 112is shown in further detail. The power management module 112 includes afirst battery monitoring module 192, a second battery monitoring module194 and a control module 196. The first battery monitoring module 192receives cell voltages, battery current, cell temperatures and/or stringvoltage as described above in FIG. 1A. The battery monitoring module 192performs cell balancing, calculates state of charge (SOC) and/or stateof health (SOH) values for the first battery 108. The second batterymonitoring module 194 also receives cell voltages, current, celltemperatures and/or string voltage as described above in FIG. 1A. Thesecond battery monitoring module performs cell balancing, calculates SOCand/or calculates SOH for the second battery 110.

The control module 196 communicates with the first battery monitoringmodule 192 and the second battery monitoring module 194. The controlmodule 196 may also receive information such as key-on events, key-offevents, vehicle speed, engine oil temperature, drive mode events,regeneration events, e-boost events or other control information fromother vehicle controllers via the vehicle data bus 114. Key-on eventsinclude engine startups responsive to user input for an ignition system(e.g., via an ignition key, button, or switch) and automatic enginestartups. Key-on events also include expected engine startups. Thecontrol module 196 may identify an expected engine startup, for example,when an occupant enters the vehicle, when an occupant sits on a driverseat of the vehicle, when a remote entry or start signal is received(e.g., from a key fob or a wireless device, such as cell phone ortablet), or when a device (e.g., key fob or wireless device) is detectedwithin a predetermined distance of the vehicle. The control module 196may detect an occupant entry of the vehicle, for example, when adriver's door of the vehicle transitions from closed to open, asindicated by a door sensor. The control module 196 may detect anoccupant sitting on the driver seat of the vehicle, for example, basedon a signal from a seat occupancy sensor of the driver seat of thevehicle. Key-off events include engine shutdowns responsive to userinput for the ignition system (e.g., via the ignition key, button, orswitch) and automatic engine shutdowns. The control module 196 may alsoshare SOC and SOH values for the first battery 108 and the secondbattery 110 with other vehicle controllers via the vehicle data bus 114.

The control module 196 enables and disables the DC/DC converter 161. Forexample, the control module enables and disables the DC/DC buckconverter 164 and the DC/DC boost converter 162 as needed during thevarious operating modes. The control module 196 also monitors operationof the overvoltage protection circuit 160. The control module 196 alsocommunicates with the heater driver circuit 146 to controlheating/cooling of zones in the heater 142 associated with the firstbattery 108 and the second battery 110.

Referring now to FIGS. 2 and 3, usable energy is shown at 25° C. and 0°C., respectively. Internal resistance of the battery cells increases atlower temperatures and therefore a charge curve moves down and adischarge curve moves up (both corresponding to lower power). Dashedlines in this example correspond to required charge and discharge powerspecifications that will vary depending upon a particular application.Useable energy is defined by intersections of the charge and dischargecurves and the dashed lines. As can be appreciated, the second batteryhas more useable energy at 25° C. as compared to lower temperatures suchas 0° C. or −25° C.

Usable energy is defined as an amount of energy between points 2 and 4in FIG. 2. Point 2 is defined as a lowest SOC at which the specified maxdischarge power can occur without falling below the minimum specifiedpack or cell voltage. Point 4 is defined as the highest SOC at which themax specified discharge power can occur without exceeding the maximumspecified pack or cell voltage.

In FIG. 2, point 1 is defined as the lowest SOC at which max specifieddischarge power pulse can begin while achieving the full specifiedduration (width of pulse from 1-2). Point 3 is defined as the highestSOC at which max specified charge power pulse can begin while achievingthe full specified duration (width of pulse 3-4).

Referring now to FIG. 4, a method 200 estimates energy (e.g., SOC of thesecond battery) that will be required to heat the engine and start theengine using the second battery based on the ambient temperature at thekey off event. At 204, when a key off event occurs, the method continuesat 208 and checks the status of the first battery and the secondbattery. At 212, based on the ambient temperature, the method determineswhether energy needs to be moved from the first battery to the secondbattery (to heat the second battery for the next key on event and tostart the engine while staying within a predetermined SOC range). Forexample, the method may determine an estimated SOC of the second batteryat the next key on event based on the estimated temperature anddetermine whether energy needs to be moved from the first battery to thesecond battery based on whether the estimated SOC of the second batteryis within the predetermined SOC range. The method may determine to moveenergy from the second battery to the first battery, for example, whenthe estimated SOC is less than a lower (SOC) limit of the predeterminedSOC range. If energy needs to be moved as determined at 216, the methoduses the DC/DC converter 161 to move the energy from the first batteryto the second battery at 220.

Referring now to FIG. 5, a method for heating the second battery inresponse to a key on event is shown at 250. At 254, the methoddetermines whether a key on event occurs. When 254 is true, the methoddetermines whether the second battery temperature is less than apredetermined temperature threshold at 258. When 258 is true, the methodcontinues at 262 and determines whether the SOC of the second battery isbelow a predetermined state of charge SOC_(TH). When 262 is false, thesecond battery is heated to a predetermined temperature using energyfrom the second battery at 266. When 262 is true, the second battery isheated using energy from the first battery at 270.

When the temperature of the battery is greater than the predeterminedtemperature threshold as determined at 258, key on crank is enabled at274. In some examples, the method may also check to determine whetherthere is excess energy in the second battery after cranking at 278. Insome examples, excess energy may be present if the SOC of the secondbattery is greater than point 3. If 278 is true, energy is moved fromthe second battery to the first battery at 282. Otherwise when 278 isfalse, the method ends.

In some examples, the power management module 112 anticipates thetemperature of the second battery for the next key-on event. Theanticipated temperature is used to calculate the amount of energyrequired to heat the second battery from the current battery temperatureto a predetermined temperature (for example 25° C.) during the nextkey-on event with the second battery having a SOC ending between points1 and 3. In this manner, the useable energy of the second system is notdiminished by the heating process.

The energy used from the first battery is not critical to operation ofthe vehicle at key-on start and can be replenished by an alternator oncethe vehicle is started. In this manner, the second battery can bemaintained between points 1 and 3 after key-on and heating is completed.

In some examples, the estimated ambient temperature at the next key onevent can be estimated by subtracting a predetermined temperature (forexample 10° C. or another value) from the outside ambient temperature atkey-off, calculating the amount of energy required to heat the batteryto optimal temperature (say 25° C.) and moving that amount of energyfrom the first battery to the second battery.

Referring now to FIG. 6, a method 300 estimates energy that will berequired to heat the engine and start the engine using the secondbattery based on an estimated ambient temperature for the next key onevent. At 304, when a key off event occurs, the method continues at 308and checks the status of the first battery and the second battery. At312, based on the ambient temperature, the method subtracts apredetermined temperature from the ambient temperature. The methoddetermines whether energy needs to be moved from the first battery tothe second battery to heat the second battery during the next key onevent and to start the engine while staying within a predetermined SOCrange based on the estimated temperature at 316. If energy needs to bemoved as determined at 316, the method uses the DC/DC converter 161 tomove the energy from the first battery to the second battery at 320.

Referring now to FIG. 7, a method 350 estimates energy that will berequired to heat the engine and start the engine using the secondbattery by estimating ambient temperature for the next key on event atleast in part based on prior usage data. At 354, when a key off eventoccurs, the method continues at 358 and checks the status of the firstbattery and the second battery. At 362, based on the prior usage of thevehicle, the method estimates the ambient temperature for the next keyon.

For example, during the weekdays, the vehicle is typically keyed off atnight at various times and started at approximately 8 AM the next day.When the vehicle is keyed off on Tuesday night, the prior usage data mayindicate that the vehicle would be started at 8 AM on Wednesday morning.The system estimates the temperature to be 10° C. at 8 AM on Wednesday(either based on weather forecast or average seasonal temperatures at ornear the GPS or geographic location of the vehicle) and moves energyfrom the first battery to the second battery as needed.

The method determines whether energy needs to be moved from the firstbattery to the second battery to heat the second battery during the nextkey on event and to start the engine while staying within apredetermined SOC range based on the estimated temperature at 366. Ifenergy needs to be moved as determined at 366, the method uses the DC/DCconverter 161 to move the energy from the first battery to the secondbattery at 370.

Referring now to FIGS. 8 and 9, more sophisticated methods fordetermining the estimated ambient temperature at the next key on eventcan be used. For example, in FIG. 8, a method 400 determines whether akey on event occurs at 404. If 404 is true, the date, time, location andambient temperature are stored at 408. At 412, a usage pattern or modelis created based upon a plurality of key on events.

In FIG. 9, a method 420 uses the usage pattern or model to predict theambient temperature during the next key on event. At 424, the methoddetermines whether a key off event has occurred. At 428 and 430, thetime of the next key on event and the ambient temperature at the nextkey on event are estimated based upon the usage pattern or model. At434, the method checks the status of the first battery and the secondbattery. At 438, the method determines whether energy needs to be movedfrom the first battery to the second battery to heat the second batteryat the next key on event based on the estimated time and ambienttemperature determined using the usage pattern or model. If energy needsto be moved as determined at 440, energy is moved from the first batteryto the second battery using the DC/DC converter at 442.

Energy that is transferred to the second battery is used to heat thesecond battery after key-on. In some examples, if the energy estimate istoo low, the first battery participates in heating the second battery byshuttling energy from the first battery to the second battery afterkey-on (during heating). The energy is moved in a controlled mannerthough the DC/DC converter to ensure the first boardnet voltage does notdrop below the minimum specification. If the energy estimate is toohigh, some energy is shuttled back from the second battery to the firstbattery after key-on. In this manner, the second battery always ends upin the optimal SOC zone (between points 1 and 3) after heating of thesecond battery is completed.

Referring now to FIG. 10, a method 450 uses energy from the firstbattery during heating if needed or stores excess energy from the secondbattery if it is not needed for heating at the next key on. If a key onevent occurs at 454, the method maintains charge on the first battery bya predetermined amount less than a full charge capacity of the firstbattery at 458. When a key off event occurs as determined at 462, themethod checks the status of the first battery and the second battery at466. At 468, the method determines whether the state of charge of thesecond battery is higher than point 3. If 468 is true, the methoddetermines whether energy needs to be removed from the second battery(for example the energy is not needed for heating) at 470. If energyneeds to be moved as determined at 471, the method uses the DC/DCconverter 161 to move energy from the second battery to the firstbattery at 472.

If 468 is false, the method determines whether energy needs to be movedfrom the first battery to the second battery to heat the second batteryat the next key on event at 476. If energy needs to be moved asdetermined at 478, the method uses a DC/DC converter to move energy fromthe first battery to the second battery at 482.

In another example, energy is moved from the first battery to the secondbattery at key off if the SOC of the second battery is below point 3 inorder to bring the second battery to or near point 3 for the givenbattery temperature or the anticipated battery temperature. In this way,the second battery is always ready for a key-on start or a key-onheating or cooling event.

In some examples, the usage pattern and/or model may use additionalinformation such as GPS data (geographic location), historical orcurrent climate data for that geographic location, date (time of year),time of day and other parameters to estimate the most likely outsideambient temperature at the next key on.

In some examples, the control system monitors the outside ambienttemperature after key off to determine if the vehicle is parked in aprotected area (such as a garage) and shuttles the energy accordingly.In other examples, the control system learns the driving habits (timeafter key off before next key on for a given time of day, for example)and uses this information to anticipate the time and outside temperaturefor the next key on. For example, if a driver parks the vehicle atbetween 7 am and 8 am, it is usually parked outside for 9 hours. If thedriver parks the car after 9 pm, it usually stays in a garage where itis warmer for 9 hours.

In some examples, the second battery is heated without diminishing thespecified usable energy of the second battery. This can be done byutilizing energy in the first battery which is not critical for fullfunctionality at key on start and is easily replenished by thealternator after key on start. In FIG. 10, if key-off occurs when theSOC is higher than point 3, the energy is dissipated from the secondbattery so that the second battery is in the optimal SOC zone after thenext key-on event. This energy is available for heating of the secondbattery. If the second battery does not need to be heated, the excessenergy is moved to the first battery.

Storage for the energy can be ensured by upsizing the first battery andcharging the battery to a level less than the capacity of the battery.In a first example, the first battery is upsized from a first capacity(such as 40-80 Ah) by an additional capacity (such as 5-20 Ah). Forexample, the first battery with a capacity of 60 Ah can be replaced by abattery having a capacity of 75 Ah to allow heating of the battery from−25C to 25C, which requires 14.3 Ah. The additional capacity cancorrespond to the amount of heating energy required for the secondbattery. During operation, the first battery is charged to the totalcapacity less the additional capacity. This ensures the first battery isalways ready to receive the additional capacity from the second battery.

In a second example, the first battery is upsized with additionalcapacity based on the amount of energy between points 3 and 4. The firstbattery is charged to the total capacity less the additional capacity.This ensures the first battery is always ready to receive the energy ofa full charge pulse (energy between points 3 and 4) from the secondbattery. This also ensures the second battery will always be able toreceive a full charge pulse after the next key-on.

Referring now to FIG. 11, a method 500 for moving energy from the firstbattery to the second battery based on the SOC of the second battery isshown. The method determines whether a key on event occurs at 504. At508, the method maintains charge on the first battery during operation.In some examples, the charges maintained at the total capacity less theadditional capacity At 512, the method determines whether a key offevent occurs. If 512 is true, the method checks the status of the firstbattery and the second battery at 516. At 518, the method determineswhether the SOC of second battery is lower than point 1. If 518 is true,the method moves energy from the first battery to the second batteryuntil the second battery is at point 1 or a greater SOC at 524.

If the SOC is below point 1, energy is shuttled from the first batteryto the second battery until the second battery is at point 1 or greaterSOC. In this manner, a max discharge power pulse can occur after thenext key on event for the full specified duration (width of pulse from1-2) without hitting the minimum specified pack or cell voltage (usableenergy). Since the first battery does not perform key-on start, it doesnot need to be at full SOC at key-on. For the examples described above,the capacity of the first battery falls below the total capacity lessthe additional capacity (e.g. 60 Ah) after key-off. The alternator wouldcharge the first battery back to 60 Ah after key-on.

Likewise, if the SOC is above point 3, energy is moved from the secondbattery to the first battery until the second battery is at point 3 orlower SOC. In this manner, a max charge power pulse can occur after keyon for the full specified duration (width of pulse from 3-4) withouthitting the maximum specified pack or cell voltage (usable energy). Forthe examples described above, the capacity of the first battery isincreased above the total capacity less the additional capacity (e.g.above 60 Ah) after key-off. If the SOC of the second battery was atpoint 4 at key-off, the first battery capacity is increased from 60 Ahto the amount of energy between points 3 and 4 after key-off. This wouldensure the second battery will always be able to receive a full chargepulse after the next key-on.

Referring now to FIG. 12, a method 550 compares the estimated ambienttemperature for the next key on event (determined at the last key offevent) to the actual ambient temperature when the key on event occurs.The method selectively uses the energy in the first battery and/or thesecond battery to heat the second battery depending upon the comparison.At 554, the method determines whether a key on event occurs. If 554 istrue, the method checks the status of the first battery and the secondbattery and other conditions such as the actual ambient temperature at558.

At 562, the method compares the actual ambient temperature to theestimated ambient temperature (previously estimated at the last key offevent). If the estimated ambient temperature is greater than or equal tothe actual ambient temperature, then the energy in the second battery issufficient to heat the second battery. If the estimated ambienttemperature is less than the actual ambient temperature, then the energyin the second battery is supplemented by the energy in the first batteryto heat the second battery. In other words, additional heating isrequired.

If 564 is true, the method continues at 570 and energy in the secondbattery is used to heat the second battery. If 564 is false, the methodcontinues at 568 and uses energy in both the first battery and thesecond battery to heat the second battery.

The systems and methods described herein allow the first battery toassist during heating after key-on if the estimated temperature atkey-on was too high (energy for heating was too low). However, sincemost of the heating energy was transferred just after key off, the loadand subsequent voltage drop of the first battery during start will beminimal, which protects the stability of the first boardnet. Thetransfer of energy is performed in a controlled manner though the DC/DCconverter to ensure the first boardnet voltage does not drop below theminimum specification. The first battery may be oversized in capacity bythe amount of heating energy required for the second battery.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. It should be understood thatone or more steps within a method may be executed in different order (orconcurrently) without altering the principles of the present disclosure.Further, although each of the embodiments is described above as havingcertain features, any one or more of those features described withrespect to any embodiment of the disclosure can be implemented in and/orcombined with features of any of the other embodiments, even if thatcombination is not explicitly described. In other words, the describedembodiments are not mutually exclusive, and permutations of one or moreembodiments with one another remain within the scope of this disclosure.

Spatial and functional relationships between elements (for example,between modules, circuit elements, semiconductor layers, etc.) aredescribed using various terms, including “connected,” “engaged,”“coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and“disposed.” Unless explicitly described as being “direct,” when arelationship between first and second elements is described in the abovedisclosure, that relationship can be a direct relationship where noother intervening elements are present between the first and secondelements, but can also be an indirect relationship where one or moreintervening elements are present (either spatially or functionally)between the first and second elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A OR BOR C), using a non-exclusive logical OR, and should not be construed tomean “at least one of A, at least one of B, and at least one of C.”

In this application, including the definitions below, the term “module”or the term “controller” may be replaced with the term “circuit.” Theterm “module” may refer to, be part of, or include: an ApplicationSpecific Integrated Circuit (ASIC); a digital, analog, or mixedanalog/digital discrete circuit; a digital, analog, or mixedanalog/digital integrated circuit; a combinational logic circuit; afield programmable gate array (FPGA); a processor circuit (shared,dedicated, or group) that executes code; a memory circuit (shared,dedicated, or group) that stores code executed by the processor circuit;other suitable hardware components that provide the describedfunctionality; or a combination of some or all of the above, such as ina system-on-chip.

The module may include one or more interface circuits. In some examples,the interface circuits may include wired or wireless interfaces that areconnected to a local area network (LAN), the Internet, a wide areanetwork (WAN), or combinations thereof. The functionality of any givenmodule of the present disclosure may be distributed among multiplemodules that are connected via interface circuits. For example, multiplemodules may allow load balancing. In a further example, a server (alsoknown as remote, or cloud) module may accomplish some functionality onbehalf of a client module.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. The term shared processor circuitencompasses a single processor circuit that executes some or all codefrom multiple modules. The term group processor circuit encompasses aprocessor circuit that, in combination with additional processorcircuits, executes some or all code from one or more modules. Referencesto multiple processor circuits encompass multiple processor circuits ondiscrete dies, multiple processor circuits on a single die, multiplecores of a single processor circuit, multiple threads of a singleprocessor circuit, or a combination of the above. The term shared memorycircuit encompasses a single memory circuit that stores some or all codefrom multiple modules. The term group memory circuit encompasses amemory circuit that, in combination with additional memories, storessome or all code from one or more modules.

The term memory circuit is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium may therefore be considered tangible and non-transitory.Non-limiting examples of a non-transitory, tangible computer-readablemedium are nonvolatile memory circuits (such as a flash memory circuit,an erasable programmable read-only memory circuit, or a mask read-onlymemory circuit), volatile memory circuits (such as a static randomaccess memory circuit or a dynamic random access memory circuit),magnetic storage media (such as an analog or digital magnetic tape or ahard disk drive), and optical storage media (such as a CD, a DVD, or aBlu-ray Disc).

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks,flowchart components, and other elements described above serve assoftware specifications, which can be translated into the computerprograms by the routine work of a skilled technician or programmer.

The computer programs include processor-executable instructions that arestored on at least one non-transitory, tangible computer-readablemedium. The computer programs may also include or rely on stored data.The computer programs may encompass a basic input/output system (BIOS)that interacts with hardware of the special purpose computer, devicedrivers that interact with particular devices of the special purposecomputer, one or more operating systems, user applications, backgroundservices, background applications, etc.

The computer programs may include: (i) descriptive text to be parsed,such as HTML (hypertext markup language) or XML (extensible markuplanguage), (ii) assembly code, (iii) object code generated from sourcecode by a compiler, (iv) source code for execution by an interpreter,(v) source code for compilation and execution by a just-in-timecompiler, etc. As examples only, source code may be written using syntaxfrom languages including C, C++, C#, Objective C, Haskell, Go, SQL, R,Lisp, Java®, Fortran, Perl, Pascal, Curl, OCaml, Javascript®, HTML5,Ada, ASP (active server pages), PHP, Scala, Eiffel, Smalltalk, Erlang,Ruby, Flash®, Visual Basic®, Lua, and Python®.

What is claimed is:
 1. A power management system for a vehicle,comprising: a first battery monitoring module configured to monitor afirst state of charge (SOC) of a first battery of the vehicle, whereinthe first battery has a first nominal voltage; a second batterymonitoring module configured to monitor a second SOC of a second batteryof the vehicle, wherein the second battery has a second nominal voltagethat is greater than the first nominal voltage; and a control moduleconfigured to selectively apply power to a heater of the second batterybased on an estimated value of the second SOC of the second battery at anext startup of an engine.
 2. The power management system of claim 1further comprising a starter control module configured to selectivelyapply power to a starter of the engine from the second battery at thenext startup of the engine.
 3. The power management system of claim 1wherein the control module is configured to apply power to the heater ofthe second battery when the estimated value of the second SOC of thesecond battery at the next startup of the engine is less than apredetermined SOC.
 4. The power management system of claim 1 wherein thecontrol module is configured to: in response to a shutdown of an engineof the vehicle, determine an estimated temperature at the next startupof the engine; and determine the estimated value of the second SOC ofthe second battery based on the estimated temperature at the nextstartup of the engine.
 5. The power management system of claim 4 whereinthe control module is configured to set the estimated temperature at thenext startup of the engine based on an ambient temperature at theshutdown of the engine.
 6. The power management system of claim 4wherein the control module is configured to set the estimatedtemperature at the next startup of the engine based on an ambienttemperature obtained in response to the shutdown of the engine minus apredetermined temperature.
 7. The power management system of claim 4wherein the control module is configured to determine the estimatedtemperature at the next startup of the engine based on an averagetemperature at a location of the vehicle at the next startup of theengine.
 8. The power management system of claim 4 wherein the controlmodule is configured to determine the estimated temperature at the nextstartup of the engine based on a forecast temperature at a location ofthe vehicle at the next startup of the engine.
 9. The power managementsystem of claim 4 wherein the control module is configured to determinethe estimated temperature at the next startup of the engine based on aplurality of previous temperatures at previous startups of the engineperformed near a location of the vehicle, respectively.
 10. The powermanagement system of claim 1 wherein the control module is configuredto: in response to a shutdown of an engine of the vehicle, determine anestimated temperature at the next startup of the engine; determine anambient temperature at the next startup of the engine; and selectivelyapply power to the heater of the second battery based on a comparison ofthe estimated temperature at the next startup of the engine and theambient temperature at the next startup of the engine.
 11. The powermanagement system of claim 10 wherein the control module is configuredto selectively apply power from only the second battery to the heaterwhen the estimated temperature at the next startup of the engine isgreater than the ambient temperature at the next startup of the engine.12. The power management system of claim 10 wherein the control moduleis configured to selectively apply power from both the first battery andthe second battery to the heater when the estimated temperature at thenext startup of the engine is less than the ambient temperature at thenext startup of the engine.
 13. A power management method for a vehicle,comprising: monitoring a first state of charge (SOC) of a first batteryof the vehicle, wherein the first battery has a first nominal voltage;monitoring a second SOC of a second battery of the vehicle, wherein thesecond battery has a second nominal voltage that is greater than thefirst nominal voltage; and selectively applying power to a heater of thesecond battery based on an estimated value of the second SOC of thesecond battery at a next startup of an engine.
 14. The power managementmethod of claim 13 further comprising selectively applying power to astarter of the engine from the second battery at the next startup of theengine.
 15. The power management method of claim 13 wherein theselectively applying power to the heater includes applying power to theheater of the second battery when the estimated value of the second SOCof the second battery at the next startup of the engine is less than apredetermined SOC.
 16. The power management method of claim 13 furthercomprising: in response to a shutdown of an engine of the vehicle,determining an estimated temperature at the next startup of the engine;and determining the estimated value of the second SOC of the secondbattery based on the estimated temperature at the next startup of theengine.
 17. The power management method of claim 16 wherein thedetermining the estimated temperature includes setting the estimatedtemperature at the next startup of the engine based on an ambienttemperature at the shutdown of the engine.
 18. The power managementmethod of claim 16 wherein the determining the estimated temperatureincludes setting the estimated temperature at the next startup of theengine based on an ambient temperature obtained in response to theshutdown of the engine minus a predetermined temperature.
 19. The powermanagement method of claim 16 wherein the determining the estimatedtemperature includes determining the estimated temperature at the nextstartup of the engine based on an average temperature at a location ofthe vehicle at the next startup of the engine.
 20. The power managementmethod of claim 16 wherein the determining the estimated temperatureincludes determining the estimated temperature at the next startup ofthe engine based on a forecast temperature at a location of the vehicleat the next startup of the engine.
 21. The power management method ofclaim 16 wherein the determining the estimated temperature includesdetermining the estimated temperature at the next startup of the enginebased on a plurality of previous temperatures at previous startups ofthe engine performed near a location of the vehicle, respectively. 22.The power management method of claim 13 further comprising: in responseto a shutdown of an engine of the vehicle, determining an estimatedtemperature at the next startup of the engine; and determining anambient temperature at the next startup of the engine, wherein theselectively applying power to the heater includes selectively applyingpower to the heater of the second battery based on a comparison of theestimated temperature at the next startup of the engine and the ambienttemperature at the next startup of the engine.
 23. The power managementmethod of claim 22 wherein the selectively applying power to the heaterincludes selectively applying power from only the second battery to theheater when the estimated temperature at the next startup of the engineis greater than the ambient temperature at the next startup of theengine.
 24. The power management method of claim 22 wherein theselectively applying power to the heater includes selectively applyingpower from both the first battery and the second battery to the heaterwhen the estimated temperature at the next startup of the engine is lessthan the ambient temperature at the next startup of the engine.